Jaunty SRU - #357345 - [PATCH] eCryptfs: Larger buffer for encrypted symlink targets

[Stefan Bader]

Tim Gardner wrote:
> The following changes since commit b7875cd8f03cdfb118f64b25d3739a254c7dc168:
>   Stefan Bader (1):
>         UBUNTU: Merge Ubuntu-2.6.28-11.42
> 
Looks right as far as I can tell. ACK

> are available in the git repository at:
> 
>   git://kernel.ubuntu.com/rtg/ubuntu-jaunty lp357345
> 
> Tyler Hicks (1):
>       UBUNTU: SAUCE: (drop after 2.6.28) [PATCH] eCryptfs: Larger buffer for encrypted symlink targets
> 
>  fs/ecryptfs/inode.c |   24 ++++++++++++++++++------
>  1 files changed, 18 insertions(+), 6 deletions(-)
> From cdb33dfaf3dbf849656ebfe6833ab8cee697de7e Mon Sep 17 00:00:00 2001
> From: Tyler Hicks <tyhicks at linux.vnet.ibm.com>
> Date: Thu, 16 Apr 2009 18:35:37 -0500
> Subject: [PATCH] UBUNTU: SAUCE: (drop after 2.6.28) [PATCH] eCryptfs: Larger buffer for encrypted symlink targets
> 
> Presumably this patch will make its way into 2.6.30.
> 
> Bug: #357345
> 
> When using filename encryption with eCryptfs, the value of the symlink
> in the lower filesystem is encrypted and stored as a Tag 70 packet.
> This results in a longer symlink target than if the target value wasn't
> encrypted.
> 
> Users were reporting these messages in their syslog:
> 
> [ 45.653441] ecryptfs_parse_tag_70_packet: max_packet_size is [56]; real
> packet size is [51]
> [ 45.653444] ecryptfs_decode_and_decrypt_filename: Could not parse tag
> 70 packet from filename; copying through filename as-is
> 
> This was due to bufsiz, one the arguments in readlink(), being used to
> when allocating the buffer passed to the lower inode's readlink().
> That symlink target may be very large, but when decoded and decrypted,
> could end up being smaller than bufsize.
> 
> To fix this, the buffer passed to the lower inode's readlink() will
> always be PATH_MAX in size when filename encryption is enabled.  Any
> necessary truncation occurs after the decoding and decrypting.
> 
> Signed-off-by: Tyler Hicks <tyhicks at linux.vnet.ibm.com>
> Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
> ---
>  fs/ecryptfs/inode.c |   24 ++++++++++++++++++------
>  1 files changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
> index 82378fb..4b79e22 100644
> --- a/fs/ecryptfs/inode.c
> +++ b/fs/ecryptfs/inode.c
> @@ -657,8 +657,9 @@ static int
>  ecryptfs_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
>  {
>  	char *lower_buf;
> +	size_t lower_bufsiz;
>  	struct dentry *lower_dentry;
> -	struct ecryptfs_crypt_stat *crypt_stat;
> +	struct ecryptfs_mount_crypt_stat *mount_crypt_stat;
>  	char *plaintext_name;
>  	size_t plaintext_name_size;
>  	mm_segment_t old_fs;
> @@ -670,12 +671,21 @@ ecryptfs_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
>  		rc = -EINVAL;
>  		goto out;
>  	}
> -	crypt_stat = &ecryptfs_inode_to_private(dentry->d_inode)->crypt_stat;
> +	mount_crypt_stat = &ecryptfs_superblock_to_private(
> +						dentry->d_sb)->mount_crypt_stat;
> +	/*
> +	 * If the lower filename is encrypted, it will result in a significantly
> +	 * longer name.  If needed, truncate the name after decode and decrypt.
> +	 */
> +	if (mount_crypt_stat->flags & ECRYPTFS_GLOBAL_ENCRYPT_FILENAMES)
> +		lower_bufsiz = PATH_MAX;
> +	else
> +		lower_bufsiz = bufsiz;
>  	/* Released in this function */
> -	lower_buf = kmalloc(bufsiz, GFP_KERNEL);
> +	lower_buf = kmalloc(lower_bufsiz, GFP_KERNEL);
>  	if (lower_buf == NULL) {
>  		printk(KERN_ERR "%s: Out of memory whilst attempting to "
> -		       "kmalloc [%d] bytes\n", __func__, bufsiz);
> +		       "kmalloc [%d] bytes\n", __func__, lower_bufsiz);
>  		rc = -ENOMEM;
>  		goto out;
>  	}
> @@ -683,7 +693,7 @@ ecryptfs_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
>  	set_fs(get_ds());
>  	rc = lower_dentry->d_inode->i_op->readlink(lower_dentry,
>  						   (char __user *)lower_buf,
> -						   bufsiz);
> +						   lower_bufsiz);
>  	set_fs(old_fs);
>  	if (rc >= 0) {
>  		rc = ecryptfs_decode_and_decrypt_filename(&plaintext_name,
> @@ -696,7 +706,9 @@ ecryptfs_readlink(struct dentry *dentry, char __user *buf, int bufsiz)
>  				rc);
>  			goto out_free_lower_buf;
>  		}
> -		rc = copy_to_user(buf, plaintext_name, plaintext_name_size);
> +		/* Check for bufsiz <= 0 done in sys_readlinkat() */
> +		rc = copy_to_user(buf, plaintext_name,
> +				  min((unsigned) bufsiz, plaintext_name_size));
>  		if (rc)
>  			rc = -EFAULT;
>  		else


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